The Politics of Mission-Critical Voice

Andrew Seybold writes in his newsletter last week:

When I left FirstNet in December of 2013, the general manager and others had agreed with me that voice on the Nationwide Public Safety Broadband Network (NPSBN) would have to wait until it was a proven technology and until data/video broadband capabilities had been implemented. I was happy with this approach. It meant that investment in LMR voice systems would continue and FirstNet would have an opportunity to determine system loading for data and video, and how much capacity might be available on the spectrum to share with partners and to add Voice over LTE (VoLTE).

The Public Safety Communications Research (PSCR) folks in Boulder, Colo. are working with the LTE standards body (3GPP), which has been working on the addition of a specification to the 3GPP LTE standard to support Mission-Critical Voice (MCV) over LTE, and to come up with a standard for off-network voice and data communications (simplex, tactical, peer-to-peer communications). But the Public Safety community agreed that the most important function of the new LTE network would be to provide access to data and video and VoLTE would be added at some point. They also agreed that LMR voice systems, which are the lifeline of the first responder community, would be around for a long time to come.

Now it seems Voice over LTE hype is back in full swing. At the recent APCO event, apparently the word was that the 3GPP will add mission-critical voice to the standards by 2018, so 2018 is when it will be available for FirstNet. I have several problems with this, and that is why I am writing this article.

Now it seems Voice over LTE hype is back in full swing. At the recent APCO event, apparently the word was that the 3GPP will add mission-critical voice to the standards by 2018, so 2018 is when it will be available for FirstNet.

Looking at the non-political aspects of mission-critical voice over LTE, there are a number of issues:

1) Before we can deploy mission-critical voice there must be administrative voice services available in order to test the network and make sure voice works when it is needed.

2) Mission-critical voice is just that, mission-critical or Public Safety grade. Voice is the first and last lifeline for Public Safety and it MUST work all of the time, every time. Once it does become available on the LTE network, devices must be enabled and there must be extensive testing and verification before it is deemed ready for full-scale deployment.

3) To provide mission-critical voice, the FirstNet network MUST provide the same or better coverage than the existing Land Mobile Radio (LMR) systems today. This is a tall order, especially given the fact that FirstNet only has $7 billion and no partners to date, and the cost of a network to match the coverage of today’s Public Safety LMR voice systems could cost upwards of $15 billion to $25 billion or more.

4) Mission-critical voice must provide inbuilding coverage and there must be a fallback in case of network failure. Today LTE has no fallback mode. If a cell site or a group of cell sites are out of service, the LTE devices cannot communicate. With today’s LMR systems there is at least one fallback mode—simplex or device-to-device communications—and many LMR networks offer several levels of what I call graceful degradation. Until LTE can provide truly robust off-network voice it cannot be considered as mission-critical in any sense of the word.

5) I am told by some very talented LTE vendor engineers and engineers at the major commercial networks that adding voice to an LTE network requires additional resources to be deployed within the network in terms of back-end infrastructure and additional cell sites. This all comes at a cost and needs to be weighed against the anticipated benefits.

6) There must be a common air interface standard. Today, Push-To-Talk (PTT) over LTE is available from the three largest U.S. network operators and a score of other players that offer cross-network PTT services. Some of these systems work pretty well and are being used today for non-mission-critical PTT. Further, many of these PTT solutions are being deployed with an IP bridge between the commercial network and LMR systems in order to provide communications to and from the LMR systems. However, no one standard has emerged and, in fact, none of the solutions I have tested and used are compatible with PTT services offered by others. It would create severe interoperability issues if either administrative or mission-critical PTT were permitted on the NPSBN before there is a fully defined, approved, and well tested industry standard for PTT. This is what the 3GPP is working on but there could be significant differences between the vision of a standards organization made up of commercial vendors and network operators and the actual requirements of the Public Safety community.

7) Mission-critical voice must be able to support true dispatch capability, in many cases, with multiple zones to mimic the LMR systems in major cities that are broken into zones or districts, usually with one of more citywide voice capabilities. Today this is accomplished using different LMR channels or with different talk groups in an LMR trunked radio system but this capability needs to be built into any LTE mission-critical voice system.

8) Other capabilities that must be provided for include talk groups that can be pre-defined or defined on the fly and multiple talk groups made up of different members. Finally, off-network voice, which is critical for Public Safety, must be robust, easy-to-use, and capable of being used while units are still within network coverage as well as when they are outside the LTE coverage area.

9) There are more capabilities that are required but to me the final test for any PTT technology or system is how quickly a user can talk on the system after pushing a PTT button, and how soon the others listening to that “channel” receive that transmission. My test for a PTT system is still the same one I have been using for years—push the button and say, “Don’t shoot,” and make sure the first word is not lost due to system timing.

10) Public Safety cannot tolerate any delay in voice communications. The idea of pushing the PTT button and waiting for a “beep” in order to talk is probably okay since that is how many of today’s LMR trunked systems operate. However, what is NOT acceptable is hearing a system busy tone—EVER!

11) PTT MUST be a one-handed operation. Today on many of the commercial PTT systems if you are using a smartphone you have to hold the phone in one hand and “push” a button on the touchscreen. This is totally unacceptable for Public Safety.

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